#include<bits/stdc++.h>
using namespace std;
class _ADD
{
public:
    string addStrings(string num1, string num2)
    {
        string str;
        int end1 = num1.size() - 1, end2 = num2.size() - 1;
        int next = 0; // next：进位
        while (end1 >= 0 || end2 >= 0)
        {
            int x1 = end1 >= 0 ? num1[end1] - '0' : 0;
            int x2 = end2 >= 0 ? num2[end2] - '0' : 0;
            end1--, end2--;
            int ret = x1 + x2 + next;
            next = ret / 10;
            ret %= 10;

            str.insert(str.begin(), '0' + ret);
        }
        if (next > 0)
            str.insert(str.begin(), '0' + next);
        return str;
    }
};

int main()
{
    return 0;
}